1. Field of the Invention
The present invention relates to the use of polymeric additives comprised of the reaction product of a carboxylic acid polymer such as polyacrylic acid and a polyether of one or more C.sub.2 -C.sub.4 epoxides as additives for cement. The invention also pertains to cement compositions containing these additives. The additives function as water reducers and super plasticizers.
2. Description of the Prior Art
Additives for cement to increase the fluidity of cement paste, mortars and concretes have been known and in use for many years. These additives are also known as water reducers because they allow less water to be used in a mortar or concrete without loss of slump (a measure of consistency or workability). This class of cement additives permits the use of less water to obtain the same slump, or the attainment of a higher slump at a given water content, or the use of less portland cement to realize the same compressive strength. The performance requirements for water reducing admixtures are specified in ASTM Method C494-92, "Standard Specifications for Chemical Admixtures for Concrete."
In ASTM C494-92, a water reducing admixture is defined as an admixture that reduces the quantity of mixing water required to produce concrete of a given consistency by at least 5%.
A high range water reducing admixture, also known as a superplasticizer, reduces the quantity of mixing water required to produce concrete of a given consistency by 12% or greater. Commercial water reducing admixtures include lignin sulfonates and naphthalene sulfonate-formaldehyde condensates. More recently, new classes of flow enhancers or water reducers have been described. U.S. Pat. No. 4,814,014 describes a cement composition containing a graft co-polymer containing a polymeric backbone moiety and polymeric side chain moieties wherein one of the polymeric moieties is a polyether moiety and the other is a non-polyether formed by polymerization of ethylenically unsaturated monomers. U.S. Pat. No. 5,393,343 describes a cement composition containing an imidized acrylic polymer made, for example, by reacting a polyacrylic acid of 2000 molecular weight with a polyethylene polypropylene oxide polymer of 2000 molecular weight terminated at one end by a primary amine group and at the other end by a methyl group.
The compositions of the prior art have not, however, been entirely satisfactory leaving much room for improvement.